Yep, that's right--stereoscopic image-pairs are easy to produce on a
flatbed scanner.

I wish I had thought of this myself--but, like almost everyone else
who uses flatbed scanners, I just didn't think enough about they work.
Richard Schubert did.

Yesterday (8 October 1998) Benton.Holzwarth sent an email message in
which he included a link to a web page in Germany, http://www.stereoscopicscanning.de
, set up by Richard Schubert--and clicking on that link really got me
fired
up. Try it and see for yourself.

Here's how it works: The scanner has a fluorescent tube that
produces
what we think of as a "bar" of light extending from one side of the
scanner
to the other as the scan head tracks the length of the glass. I
thinik
that's what fools us into thinking that the scanner's sensor
extends
all the way across the glass, like the light. It doesn't.
It's
fed by a small lens in the center of the scan head. What that
means--and
what we don't think about--is that there's parallax in scanned
images.
We don't ordinarily notice it because we scan flat
things.
But scan a 3-D object, and that parallax suddenly becomes apparent.

What Richard Schubert realized is that if you scan an object twice,
once with it placed to the right of the lens and again with it to the
left,
you get two different images--because of the parallax.

When you look at one of the scanned images with the right eye and
the
other with the left eye, you see the object in three
dimensions--stereoscopically!

Of course I had to try it right away. Some of my experiments
are
below. (If you haven't tried looking at stereograms before, you
might
want to read the Viewing Tips first.)

NOTE: These links open in a
new window.
If you leave it open, then the other links will open in it, too.
You can use this page as a menu.

VIEWING TIPS
You can perceive the stereoscopic effect with no special equipment
either by crossing your eyes or by letting them diverge, to go
wall-eyed.
Which way you do it depends on which scanned image is on which side. In
most of my experiments here, there are three images--but they're really
two image-pairs, one for the walleye method and the other for the
crosseye
method. The center image is in both pairs, and the two side
images
are identical.

It's a little tricky at first to get the hang of perceiving
steroeoscopically.
For the "walleye" method, you can use two rolled up sheets of paper (or
toiletpaper tubes) to guide each eye to see only one of the
images.
Then sort of gaze at them without trying to focus sharply, until they
merge
into one image. Then you should begin to perceive it in three
dimensions.
Without the tubes, you can do the same thing. Let your eyes relax
as if you were looking at something beyond the screen, until
you
start to see three images. Then try to sort of pay attention to
the middle one, without really focusing on it. After a little
while
it will sort of lock in, and you'll suddenly know that it has depth.

For the crosseye method, you can hold a fingertip (or a pencil or
the
like) about halfway between your eyes and the image pair. Focus
on
the fingertip, but be aware of the images behind it.
After
a while, you'll become aware that there's a third apparent image
between
the real ones, and eventually you should realize that it has depth.

Important: To see the stereo effect, you must be able to see
clearly
with both eyes. The images must be in focus with each eye.
You may need to wear reading glasses.